This invention pertains to the art of cable support structures and more particularly to a cable support assembly for a fiber optic cable and method of stringing same.
The invention is particularly applicable to an all dielectric cable support assembly and will be described with reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in supporting and stringing other cables with equal success.
The proven performance of optical fibers has resulted in an increasing use of fiber optic cables for data transmission. Fiber optic cables, though, require special handling as a result of the fragile optical fibers contained therein. Additionally, beyond the mere mechanical gripping problems that must be overcome, it is necessary to protect the fiber optic cable against electrical degradation created by strong electrical fields of nearby energized cables.
Suspension from poles or other support structures subjects cables to both dynamic and static stresses. The weight of the cable being suspended at only selected points along its longitudinal extent is the principal component of the static stress. The dynamic stress primarily arises from oscillation of the fiber optic cable. For example, aeolian vibration is a natural response resulting from wind vortices passing over the suspended cable. Oscillation of the cable can lead to fatigue damage as a result of repeated flexural bending. Some latitude must be provided by the support structure to permit limited oscillation of the cable without the adverse effect of flexural fatigue.
Other support devices do not adequately accommodate the stringing, initial, or final sag of the cable. Although a cable extends axially through the support member, it is necessary to incorporate a predetermined sag of the cable from one pole to the next pole. The amount of sag, and likewise the sag angle, will change with different temperatures and field conditions, such as the terrain and spacing between poles.
Ideally, a cable will extend in a straight line whenever possible to minimize load factors on the support members. Unfortunately, the cable must curve or deviate from its longitudinal extent. If the deviation from a straight line is not factored into the support member structure, abrasion of the fiber optic cable can result. Again, prior art devices have not adequately accommodated for less than ideal conditions encountered in the field.
Still another difficulty encountered with prior art support devices results from temporarily stringing the cable before final suspension adjustments are made. Typically, temporary supports are used for the initial stringing of the cable. Thereafter, separate, permanent support members are mounted to an associated structure such as a pole to receive the cable. The temporary supports may then be removed once the permanent support members are in place.
This method necessarily requires that at least an extra step be undertaken in order to suspend the cables. That is, the temporary support must also be secured to the pole and then removed once the permanent support members are in place. This involves a waste of time, labor, and material all at an increased cost to the consumer.
The subject invention is deemed to provide a reliable support structure particularly adapted for fiber optic cables and overcome the above-noted shortcomings of the prior art.